Balancing Rod Assemblies
Thread Starter
Melting Slicks
Joined: Oct 2013
Posts: 2,569
Likes: 126
From: San Diego California
Balancing Rod Assemblies
1973 350/190 hp.
In the picture, I've already ground the sides (Arrow) but need to go more (another .2 oz.). I'm wondering about the tabs I've got circled. They seem to serve no purpose as far as structural support/function.
Is it an acceptable practice to grind these tabs for lightening the assemblies?
Thanks in advance.
Steve
In the picture, I've already ground the sides (Arrow) but need to go more (another .2 oz.). I'm wondering about the tabs I've got circled. They seem to serve no purpose as far as structural support/function.
Is it an acceptable practice to grind these tabs for lightening the assemblies?
Thanks in advance.
Steve
Racer
Joined: Jan 2015
Posts: 293
Likes: 43
From: Vernon B.C.
Those tabs are for splashing oil on the cylinder walls. I have removed them in the past with no ill effects. 2 oz is a lot to remove. You are removing the piston from the rod to do this right? Your going to have to weight match the rods big ends and small ends. I would find the lightest rod and make it as light as I can and then match to that one. Good luck on your project!
Limping across the line
Joined: Oct 2002
Posts: 5,299
Likes: 109
From: Peoria Az
Steve to truly be helpful we need to know that you're doing this correctly.
! pistons are weighed with the rings seperately from the rods.
All Pistons should be brought down to the weight of the lightest piston.
Beams of the rods are polished / ground lengthwise if you grind across you're weakening the rod.
The rods have weight blocks on each end that you grind away for balancing. That big hunk of mass you see at the end of the rod cap is what you grind,same is on the small end.
Each end of the rod has to be weighed. . this takes a special fixture/machine. balance each end to the other rods.
those tabs you see are for flinging oil to splash lube the camshaft and cylinder walls. leave them there.
! pistons are weighed with the rings seperately from the rods.
All Pistons should be brought down to the weight of the lightest piston.
Beams of the rods are polished / ground lengthwise if you grind across you're weakening the rod.
The rods have weight blocks on each end that you grind away for balancing. That big hunk of mass you see at the end of the rod cap is what you grind,same is on the small end.
Each end of the rod has to be weighed. . this takes a special fixture/machine. balance each end to the other rods.
those tabs you see are for flinging oil to splash lube the camshaft and cylinder walls. leave them there.
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
Steve to truly be helpful we need to know that you're doing this correctly.
! pistons are weighed with the rings seperately from the rods.
All Pistons should be brought down to the weight of the lightest piston.
Beams of the rods are polished / ground lengthwise if you grind across you're weakening the rod.
The rods have weight blocks on each end that you grind away for balancing. That big hunk of mass you see at the end of the rod cap is what you grind,same is on the small end.
Each end of the rod has to be weighed. . this takes a special fixture/machine. balance each end to the other rods.
those tabs you see are for flinging oil to splash lube the camshaft and cylinder walls. leave them there.
! pistons are weighed with the rings seperately from the rods.
All Pistons should be brought down to the weight of the lightest piston.
Beams of the rods are polished / ground lengthwise if you grind across you're weakening the rod.
The rods have weight blocks on each end that you grind away for balancing. That big hunk of mass you see at the end of the rod cap is what you grind,same is on the small end.
Each end of the rod has to be weighed. . this takes a special fixture/machine. balance each end to the other rods.
those tabs you see are for flinging oil to splash lube the camshaft and cylinder walls. leave them there.
Match the big and small rod ends to the lightest ones, which IMOE aren't necessarily both going to be on the overall lightest rod.
Team Owner
Joined: May 2001
Posts: 87,302
Likes: 1,583
From: Western NY
Those tabs are for splashing oil on the cylinder walls. I have removed them in the past with no ill effects. 2 oz is a lot to remove. You are removing the piston from the rod to do this right? Your going to have to weight match the rods big ends and small ends. I would find the lightest rod and make it as light as I can and then match to that one. Good luck on your project!
You take the heaviest rod, lighten it wherever you can, by polishing the beams, etc, the match the others to it......
Burning Brakes
Joined: Jul 2015
Posts: 823
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From: Austin TX
Thread Starter
Melting Slicks
Joined: Oct 2013
Posts: 2,569
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From: San Diego California
I've just discovered why you weigh components individually, THEN use the adding machine to match the pistons, pins, and rods, all to an assembled weight that is closest to all. You'll also end up taking off minimal material that way, but here's what I found:
If you weigh the assembled units (piston, pin, rod cap & nuts and rings), and then try and match all to the lightest, you may find your heaviest one has little to no material left to remove, in order to get it close with the others.
Yeah, I'm learning. SO WHAT?!
I do appreciate the input.
Steve
Last edited by Cavu2u; Dec 12, 2015 at 05:39 PM.
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Burning Brakes
Joined: Jul 2015
Posts: 823
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From: Austin TX
When you buy the rods, they all have a full-size balance pad on top and bottom. Start by picking the lightest and matching all the others to that one. I have never seen a set where the heaviest of the lot couldn't be matched to the lightest and not have some pad material left at both ends. I suppose it's possible, but if so, it's a bad set. The alternative is to pick a compromise (heavier) weight and leave the lighter rods as-is. However, you'll end up with a set that isn't as well balanced as it could/should be. It you're patient, it's not too difficult to get all the big ends and all the small ends within a few tenths of a gram of each other.
Last edited by 454Luvr; Dec 12, 2015 at 06:22 PM.
Burning Brakes
Joined: Jul 2015
Posts: 823
Likes: 57
From: Austin TX
1973 350/190 hp.
In the picture, I've already ground the sides (Arrow) but need to go more (another .2 oz.). I'm wondering about the tabs I've got circled. They seem to serve no purpose as far as structural support/function.
Is it an acceptable practice to grind these tabs for lightening the assemblies?
Thanks in advance.
Steve
In the picture, I've already ground the sides (Arrow) but need to go more (another .2 oz.). I'm wondering about the tabs I've got circled. They seem to serve no purpose as far as structural support/function.
Is it an acceptable practice to grind these tabs for lightening the assemblies?
Thanks in advance.
Steve
Last edited by 454Luvr; Dec 12, 2015 at 06:35 PM.
Thread Starter
Melting Slicks
Joined: Oct 2013
Posts: 2,569
Likes: 126
From: San Diego California
Thanks 454,
That's exactly what I'm gonna do. Disassemble everything, except the rod caps of course, press out the wristpins, and start over. No big deal. Got a kidney transplant in July and all is well. Nothing small gets me down anymore.
Steve
That's exactly what I'm gonna do. Disassemble everything, except the rod caps of course, press out the wristpins, and start over. No big deal. Got a kidney transplant in July and all is well. Nothing small gets me down anymore.
Steve
Safety Car
Joined: Mar 2007
Posts: 3,652
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From: Bridgewater nj
Just to let you know, you really don't have to do all that weighing for a mild rebuild. I usually just weigh my new pistons and compare them to the old ones. A few grams will never be noticed but you will have a lite piston and you'll have a heavy piston. Just try matching them the best you can. Usually the machine shop will do this while pressing the pins out. If you are new at this, just go to the machine shop, it's not expensive.
Race Director
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Please do some reading on the whole balancing procedure. You balance each end of the rod and get the total correct at same time.
Are you planning on rebalancing the crank after all this metal removal? Lightening things is a good thing...but I doubt you'll be removing much overall...so probably won't affect balance..
But the cranks balance is based on the weights of all the components and whether those weights are rotational or reciprocal.
Is this a stock motor you're just wanting to play with? Not sure what we're gaining here...
JIM
Are you planning on rebalancing the crank after all this metal removal? Lightening things is a good thing...but I doubt you'll be removing much overall...so probably won't affect balance..
But the cranks balance is based on the weights of all the components and whether those weights are rotational or reciprocal.
Is this a stock motor you're just wanting to play with? Not sure what we're gaining here...
JIM
Thread Starter
Melting Slicks
Joined: Oct 2013
Posts: 2,569
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From: San Diego California
Just to let you know, you really don't have to do all that weighing for a mild rebuild. I usually just weigh my new pistons and compare them to the old ones. A few grams will never be noticed but you will have a lite piston and you'll have a heavy piston. Just try matching them the best you can. Usually the machine shop will do this while pressing the pins out. If you are new at this, just go to the machine shop, it's not expensive.
Suppose two assemblies are a few grams heavy. Which journals/cylinders would they go on to minimize the effect of their weight, if any? I'd assume the more directly opposed they are to each other would minimize their effect to each other, but wreak a bit with all others, no?
Steve
Thread Starter
Melting Slicks
Joined: Oct 2013
Posts: 2,569
Likes: 126
From: San Diego California
Please do some reading on the whole balancing procedure. You balance each end of the rod and get the total correct at same time.
Are you planning on rebalancing the crank after all this metal removal? Lightening things is a good thing...but I doubt you'll be removing much overall...so probably won't affect balance..
But the cranks balance is based on the weights of all the components and whether those weights are rotational or reciprocal.
Is this a stock motor you're just wanting to play with? Not sure what we're gaining here...
JIM
Are you planning on rebalancing the crank after all this metal removal? Lightening things is a good thing...but I doubt you'll be removing much overall...so probably won't affect balance..
But the cranks balance is based on the weights of all the components and whether those weights are rotational or reciprocal.
Is this a stock motor you're just wanting to play with? Not sure what we're gaining here...
JIM
It's the original block & heads that match the factory worksheet. I'm rebuilding it so it will go with the car when sold, cuz I'm just sentimental that way. The engine is the lowest horsepower version available in '73; that's the way it was, and that's the way it will be.
Just trying to restore it the best I can.
But I have to admit, the 383 that's in the car now is running really well, but, that's not the topic here.
Thanks for the feedback.
Steve
Race Director
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If I was just reusing the old pistons/rods and installing rings and bearings...I'd just leave it alone as far as balancing things. It's not going to be going high RPM so I'm sure what the factory did was close enough. You can stand a pretty big difference on a stock motor and never know the difference. If you lighten things a lot....and don't change crank balance you're "over balancing" it to some degree which is a tick used on high RPM deals. Balancing isn't exact through out the range....you'll get it correct in a certain range and it works OK. The math used to assemble bob weights makes assumptions on oil weight for example.
JIM
JIM
Le Mans Master
Joined: Oct 2002
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From: Las Vegas - Just stop perpetuating myths please.
Just weight match is fairly easy with one of these tools: http://autoplicity.com/2146775-power...FVBlfgodjPsBiw
But to measure each big and small end u need a scale and jig to hold the rod horizontal for the big end and then the small end which will be a different horizontal position. Some guys just use a couple of small boards and 2 nails in different locations to hold the one end at a time on the scale. I guess practice makes perfect here. Also it takes some patience to match each ring package and piston and rod for the same/equal weight. Not for those in a rush.
Like as Jim says accurate balance is really for high rpm and for street motors close is good enough. Like within a few grams or even more is OK. Let the 8,500rpm NASCAR builders lose thier hair - they're getting paid for it.
Good luck and let us know how it works for u steve.
But to measure each big and small end u need a scale and jig to hold the rod horizontal for the big end and then the small end which will be a different horizontal position. Some guys just use a couple of small boards and 2 nails in different locations to hold the one end at a time on the scale. I guess practice makes perfect here. Also it takes some patience to match each ring package and piston and rod for the same/equal weight. Not for those in a rush.
Like as Jim says accurate balance is really for high rpm and for street motors close is good enough. Like within a few grams or even more is OK. Let the 8,500rpm NASCAR builders lose thier hair - they're getting paid for it.
Good luck and let us know how it works for u steve.
Team Owner
Joined: May 2001
Posts: 87,302
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From: Western NY
If you start with the rod that's already the lightest, work it to lighten it some more, THEN find out that you can't get all of the remaining rods to the same weight, what are you going to do? As you said, yes, you have a set of "bad rods", but if those "bad rods" came out of your core engine, and they're all you have to work with, you have to minimize the opportunity of problems.
Therefore you take the heaviest rod, lighten it as much as possible/necessary, then match the rest to it. You can usually remove more material, if necessary, but it's tough to add more, if you've made a mistake.....
Burning Brakes
Joined: Jul 2015
Posts: 823
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From: Austin TX
THEN find out that you can't get all of the remaining rods to the same weight, what are you going to do?